This laboratory discovered a unique family of nonpolar metabolites of steroids which we named lipoidal derivatives, and subsequently showed to be fatty acid esters. They are now known to include virtually all of the families of steroid hormones. We have shown that the estrogens, estradiol (E2) and estriol (E3) are biosynthetically converted into lipoidal derivatives (LE2 and LE3 respectively) esterified with fatty acids in the D-ring. These nonpolar metabolites of the estrogens are extremely potent hormones which produce long lasting estrogenic effects. In fact they are much more potent than E2, previously believed to be the most powerful of the naturally occurring mammalian estrogens. None of the estrogen esters bind to the estrogen receptor and so the naturally occurring mammalian estrogens. None of the estrogen esters bind to the estrogen receptor and so they are incapable of direct estrogenic stimulation. They require hydrolytic activation by esterases. We have found that LE2 is synthesized and sequestered in hydrophobic tissues, such as fat, including the fat of menopausal women. The presence of this potent estrogen in women after the climacteric suggests that LE2 may play an important role in maintenance of their estrogen sensitive tissues through the enzymatic release of E2. In order to examine this hypothesis we will determine the concentration of LE2 in the fat of menopausal women and compare it to the extent of menopausal symptomatology. We postulate that they are inversely related. Excess production of these very potent and previously unmeasured hormones could be related to endocrine disorders, even cancers, for which evidence of estrogen excess exists, but for which increased hormones have not been found. Thus we will determine whether LE2 is elevated in women with endometrial cancer, a cancer known to be associated with increased aromatase in fat. To uncover their physiological role, other studies to be performed in rats, will measure the rates of synthesis and hydrolysis of the endogenous steroid in several tissues under conditions including stimulation with nonesterifiable estrogens and progestins. Large concentrations of LE2 are also present in the ovary and we will determine whether it plays an intraovarian role or whether it is secreted. While the structure of some endogenous lipoidal derivatives of steroids have been determined, none have been biologically active steroids, including estrogens. Their structures have been surmised by comparison to the lipoidal derivatives identified in in vitro biosynthetic studies; on the basis of their polarity and their chemical conversion into the free steroid by saponification. Follicular fluid from the ovaries of women stimulated with gonadotrophins contain LE2 in amounts far beyond any other tissue, approx 100 ng/ml (E2 equivalents), a concentration that enables a complete characterization of endogenous LE2. Recently we have found that LE2 in follicular fluid consists primarily of a single ester with properties unlike any we have previously found. We intend to isolate and determine the structural composition of the endogenous lipoidal derivative of estradiol in follicular fluid. This characterization will then be used to compare both biosynthetic and endogenous LE2 from different tissues, such as ovary and fat, in order to investigate their relationship to each other and the manner in which they are synthesized.